An ATV (All Terrain Vehicle) that runs on irregular grounds or all grounds, called a buggy, is a single-seat off-road vehicle having four wheels, which may be used in leisure such as hunting and trail touring or used as a farm vehicle in some cases. In such an all-ground type vehicle, as a transmission in a power transmission apparatus for transmitting power of an engine to drive wheels, manual type one is employed which performs shift operations by a driver's shift pedal operations.
The manual type transmission has a transmission input shaft or a main shaft that is coupled to a crankshaft of an engine through an input clutch to be driven by the engine and that has a plurality of drive gears mounted thereto; and a transmission output shaft or a countershaft to which a plurality of driven gears are mounted which are always engaged with the drive gears to form trains of speed change gears respectively, and a switchover sleeve of the dog clutch type that is driven by the operation of a shift pedal is provided in the transmission to select a train of speed change gears to transmit power. The manual type transmission is provided with an idler gear for reverse to back a vehicle which is engaged with a drive gear for reverse operation mounted to the main shaft and a driven gear for reverse mounted to the countershaft, and the idler gear is mounted to a reverse shaft that is arranged in a case housing therein the main shaft and the countershaft.
To prevent the idler gear mounted to the reverse shaft from slipping along the shaft direction, there is known a conventional method in which ring-shaped retention grooves are formed at the reverse shaft corresponding to both sides of the idler gear; and snap rings are mounted to the respective retention grooves to prevent the idler gear from slipping along the shaft direction. Furthermore, there is known a method disclosed in Japanese Patent Application Laid-Open Publication 10-259860 in which step portions along the diameter direction are formed on the reverse shaft corresponding to both sides of the idler gear and washers are mounted between the respective step portions and the idler gear to prevent the idler gear from slipping along the shaft direction.
However, in case of forming retention grooves for retaining two snap rings at the reverse shaft, there is required an assembling process of stretching the snap rings along the diameter direction and attaching thus stretched snap rings to the reverse shaft, which undesirably increase the number of parts as well as the number of manufacturing processes of the power transmission apparatus. Furthermore, use of washers requires cutting works for the reverse shaft to form two step portions corresponding to both sides of the idler gear. This results in increasing working processes for the reverse shaft is increased as well as in requiring two washers to be mounted to the reverse shaft, which undesirably increase the number of parts as well as the number of manufacturing processes of the power transmission apparatus accordingly.